Method and apparatus for forming ring grooves and piston lands on a steel piston, especially for internal combustion engines

ABSTRACT

A method of and apparatus for providing steel pistons with annular grooves, according to which the annular grooves are made by roll-forming the material of the piston head.

111 1119 States i atent 1 1 Elsbett et al.

METHOD AND APPARATUS FOR FORMING RING GROOVES AND PISTON LANDS ON A STEEL PISTON, ESPECIALLY FOR INTERNAL COMBUSTION ENGINES Inventor s: Gunter El s bett; Ludwig E1556,

both of Hilpoltstein, Germany Assignee: Maschi nenfabrik Augsburg-Numberg Aktiengesellschatt Werk Numberg, berg, Nu rnberg, Germany Filed: Feb. 18, 1971 Appl. No.: 116,465 1 Foreign Application Priority Data Feb. 29, 1970 Germany .f. ..P 20 07 647.5

U.S. Cl ..72/107, 72/110, 29/1565 R Int. Cl. ..B2lh 1/00, B21h 7/18 Field of Search....72/71, 80,107, 108, 109, 110, 72/121;29/156.5 R

Jan. 23, 1973 References Cited UNITED STATES PATENTS 2,595,668 5/1952 Getty ..72/121 3,473,358 10/1969 Marcovitch ..72/121 FOREIGN PATENTS OR APPLICATIONS 701,881 1/1941 Germany ..29/156.5

Primary Examiner-Lowe11 A. Larson Attorney-Walter Becker [57] ABSTRACT A method of and apparatus for providing steel pistons with annular grooves, according to which the annular grooves are made by roll-forming the material of the piston head.

6 Claims, 7 Drawing Figures PATENTEU JAN 23 I973 INVENTORS GUNTER ELSBETT LUDWIG ELSBETT FIG-4 METHOD AND APPARATUS FOR FORMING RING GROOVES AND PISTON LANDS ON A STEEL PISTON, ESPECIALLY FOR INTERNAL COMBUSTION ENGINES This invention relates to engines, specifically internal combustion engines, having pistons whose heads are fitted with piston rings to provide a gas-tight seal for the combustion space. In order to enable the piston rings to be locatedon the piston head, each head has a separate groove for each piston ring. In conventional practice, each ring groove, preferably of rectangular cross-section, is machined from the solid on the lathe using square-ended tools. Great importance is attached to obtaining smooth groove faces in order to provide accurate guidance of the piston ring which flexes in the groove. In this orthodox method of making the ring groove, it is considered to be a draw-back that where the piston material is of non-uniform hardness, the lathe tool will tend to wander off causing a wavy groove which is the source of gas and/or oil leakages. Moreover, it is difficult to obtain a surface finish of the machined faces that will ensure a good sealing effect against the piston ring. In addition, the service life of the ring groove depends on the degree of strain hardening of the ring groove sides.

This invention has for its object to provide an improved method, and apparatus to implement the method, for making ring grooves and piston lands in a manner, firstly, to ensure a high surface finish, accurate form and high strength and secondly to impart to the piston a special shape, e.g., an elliptical cross-section and/or a top-to-bottom taper, so that the shape of piston when hot will match that of the engine cylinder.

The process employed according to the present invention to achieve these objects consists in producing the ring grooves in and/or the piston lands on the sealing face of the piston head by roll-forming.

According to a further feature of this invention, the method proposed for making, for instance, the ring grooves, can be used to roll-form several ring grooves in the piston head at the same time.

The method according to this invention is carried out by means of apparatus, which is also the object of this invention, comprising rolls applied against the head of the piston including firstly, a roll for making ring grooves and, secondly, a roll for shaping the piston lands, the former being of a size corresponding to the width and depth of the ring groove to be made and the latter being shaped with a width and displacement required to give the desired shape of the sealing face of the piston.

Where it is desired to form, say, all ring grooves at the same time in the head of the piston, it is a further feature of the apparatus according to this invention to have several rolls corresponding to the desired ring groove shape working in parallel.

According to a further feature of this invention, each roll can be formed with at least one projection on is circumference.

ln orderto reduce the time required for making, say, the ring groove, the apparatus according to a further feature of the invention can consist of several rolls arranged concentrically about the piston head, the rolls working in tandem in successive steps in the same ring groove which may be made in solid or preformed material.

Where roll-forming of the ring grooves is carried out simultaneously with the roll-forming of the lands on the piston head, it being irrelevant whether the piston revolves or the roll apparatus revolves about the piston, the apparatus according to a further feature of the invention can be arranged so that it combines in one unit both the rolls for making the ring grooves and the roll or rolls for shaping the lands of the piston head.

The method according to this invention and the apparatus proposed to implement this method permit ring grooves and/or the shape of the piston lands to be formed within a minimum of time and with minimum tool wear. As a result, production costs of massproduced pistons can be reduced substantially without sacrificing the quality of the ring grooves made or accuracy of the shape of the piston lands obtained. Another advantage of this invention is in the fact that roll-forming of the ring grooves and/or the shape of the lands on the piston head results in strain hardening of the material, especially in the region of the ring grooves, whereby improved sliding contact is ensured with the piston rings.

As a typical embodiment of the invention, the ac companying schematic drawing shows by way of example the method of roll-forming the ring grooves in the head of a piston.

FIGS. 1 and la are longitudinal central sections through a piston head with the rolls withdrawn from the finished ring grooves,

FIG. 2 is a plan view of the piston head with several rolls arranged concentrically about it,

FIG. 3 is an enlarged elevation of a roll formed with a projection on the center of its circumference,

FIG. 4 is an enlarged view of a roll formed with two projections on its circumference,

FIG. 5 is an enlarged view of a roll formed with an laterally off-set projection on its circumference and FIG. 6 is an enlarged view of a gang-type roll assembly comprising several rolls working in parallel.

The method of making ring grooves 1 to 3 is illustrated by the example of a steel piston 4 for internal combustion engines, for instance Diesel engines. The apparatus serving for implementing said method comprises at least one roll 5 formed to match the ring groove 1, 2 or 3 to be made and attached to a machine not shown in the drawing, the roll or rolls being arranged to be pressed into the solid, or pre-machined, sealing face 6 of the piston head at a preset feed rate.

In the embodiment illustrated in FIGS. 1 and 2, the piston 4 is held in clamping means 7, of which only the outline is shown in the drawing, by means of which the piston can be rotated about its longitudinal centerline x. The roll 5 forming the respective ring groove 1, 2 or 3 in the head 6 of the piston 4 is rotatably fitted on a mountingdevice which in turn is mounted on a carriage or screw mechanism providing the feed motion. The carriage or screw feed mechanism is arranged to provide the feed motion at a rate to suit the material of piston 4 to be formed, the roll 5 fitted to the device on the carriage or screw feed mechanism gradually entering the solid or pre-machined body of the piston head 6. Due to the fact that the roll 5 for the ring groove 1, 2 or 3 to be made is of corresponding shape and size, the desired ring groove is made in one operation as the roll is forced into the piston, whereby the need for subsequent finishing operations on the ring groove is eliminated. Depending on the design of the roll 5, this can be formed with one central projection (FIG. 3) on its circumference or can have 2 projections 11 (FIG. 4) arranged symmetrically relative to its centerline z. Obviously, the roll 5 can be formed with only one asymmetrical projection 12 as shown in FIG. 5. In order to reduce the time required for making the ring grooves l, 2 and 3, several rolls 5 can be arranged concentrically about the head 6 of the piston, these rolls being arranged in tandem on the mounting device to work the same ring groove 1, 2 or 3. This type of arrangement with several rolls 5 is shown schematically in FIG. 2.

Also with a view to reducing the time for making the ring grooves l to 3, it is possible to have several rolls 5 to n, i.e., a gang of rolls arranged on each mounting device with one roll 5 forming one ring groove 1 and the adjacent roll 5 of the gang rolls forming the next ring groove 2, etc. The rolls 5 to n of such gang rolls can be arranged on the same mounting device so as to enter the solid or premachined sealing face of the piston head 6 and be withdrawn from the ring grooves l to 3 on completion simultaneously.

Since, with a view to reducing weight, the pistons 4 are commonly made of a core part 8 and a land portion 9 enveloping the core partly, it is possible and often desirable for reasons of strength, to use grip type clamping means 7 to hold the piston, the grips filling roughly the space between the core section 8 and the land portion 9. This enables the rolls 5 or gang rolls 5 n to enter into the piston land 6 at a faster rate since this land portion is adequately supported by the grips 7 to prevent deformation.

Depending on the design of the roll mounting system, either the rolls 5 or gang rolls 5 n can be revolved around the piston head 6, or the piston 4 can be made to rotate about its longitudinal axis x. The radial feed of the rolls 5 into the piston head 6 or withdrawal of the rolls away from the piston (arrow direction P) is normally a function of the rotating motion of the piston 4 in a manner that an appropriate feed motion of the rolls takes place on completion of every 360 rotation of the piston. Naturally, it is possible to use a converse arrangement. In such a case, the piston 4 will be stationary and the rolls 5 or gang rolls 5 n will be arranged to rotate about their centers y as well as revolve about the stationary piston 4.

Forming the lands of piston 4 can be effected by individual or several rolls in parallel. Since forming the piston lands with, say, an elliptical shape and/or a taper involves flattening portions of the cylindrical surface and no penetration into the face of the piston head 6, it is possible to use calender type rolls, i.e., rolls without any projections. Apart from providing the piston with, say, a top-to-bottom taper and an elliptical cross-section, the piston can be formed with local depressions on the piston lands or sealing face (for instance to suit the honing pattern of the cylinder). In order to reduce production time for the piston 4, shaping of the piston lands can be carried out at the same time as shaping the ring grooves l to 3 or 1 to n respectively. For this purpose, the roll for forming the piston lands can be combined with the rolls 5 to n for the ring grooves I to 3 in one gang roll unit, the roll for the lands being formed on its surface with the negative of the desired piston head shape.

Four rolls 13 for piston lands are shown by dasheddot lines in FIGS. 1 and 2, these rolls combining to produce the desired shape of the piston sealing face. The rolls 13 are mounted on separate shaft or axle and can be forced on to the piston head 6 either alone or together with the rolls 5 to n.

What we claim is:

1. An apparatus for roll forming groove and land areas in heads of steel pistons for internal combustion engines, especially diesel engines, which comprises: first roll means having an axial dimension at the periphery corresponding to the axial dimension of a ring groove to be formed thereby and adapted to be pressed into the periphery of a steel piston head during rotation of the piston head and roll means to form a ring groove in the piston head, and second roll means adapted to engage the periphery of the said piston head for forming the land areas thereon disposed on opposite axial sides of said groove.

2. An apparatus according to claim 1 in which first roll means comprises a plurality of rolls in axially spaced relation operable to form a plurality of axially related ring grooves in said piston head simultaneously.

3. An apparatus according to claim 1 in which said first roll means comprises at least one radially extending circumferential projection.

4. An apparatus according to claim 1 in which said first roll means comprise a plurality of rolls distributed circumferentially about the piston head.

5. An apparatus according to claim 1 in which said first roll means comprise a plurality of sets of rolls distributed circumferentially about the piston head, each set of rolls comprising a plurality of rolls distributed axially of said piston head.

6. An apparatus according to claim 5 in which said second roll means comprises land forming rolls interposed between said sets of rolls and adapted to be applied to said piston head simultaneously with said sets of rolls. 

1. An apparatus for roll forming groove and land areas in heads of steel pistons for internal combustion engines, especially diesel engines, which comprises: first roll means having an axial dimension at the periphery corresponding to the axial dimension of a ring groove to be formed thereby and adapted to be pressed into the periphery of a steel piston head during rotation of the piston head and roll means to form a ring groove in the piston head, and second roll means adapted to engage the periphery of the said piston head for forming the land areas thereon disposed on opposite axial sides of said groove.
 2. AN apparatus according to claim 1 in which first roll means comprises a plurality of rolls in axially spaced relation operable to form a plurality of axially related ring grooves in said piston head simultaneously.
 3. An apparatus according to claim 1 in which said first roll means comprises at least one radially extending circumferential projection.
 4. An apparatus according to claim 1 in which said first roll means comprise a plurality of rolls distributed circumferentially about the piston head.
 5. An apparatus according to claim 1 in which said first roll means comprise a plurality of sets of rolls distributed circumferentially about the piston head, each set of rolls comprising a plurality of rolls distributed axially of said piston head.
 6. An apparatus according to claim 5 in which said second roll means comprises land forming rolls interposed between said sets of rolls and adapted to be applied to said piston head simultaneously with said sets of rolls. 